Embodiments of the present invention relate generally to medical imaging systems, and more particularly, to medical imaging systems displaying strain information related to an imaged heart.
Ultrasound systems are used in a variety of applications and by individuals with varied levels of skill. In many examinations, operators of the ultrasound system provide inputs used by the system to process the information for later analysis. Once processed, the information may be displayed in different formats. For example, the processed information may be displayed in different charts and/or plots showing quantitative parameters or values. For example, strain values based on myocardial deformation (e.g., systolic and/or diastolic compression/expansion of the heart wall) due to cardiac ejection and/or filling may be plotted on a bullseye display. Using the bullseye display, which is typically segmented into a plurality of segments, quantitative assessment of regional myocardial function may be performed. The plurality of segments may correspond to a segmented model of the heart having radial, longitudinal and circumferential coordinates.
Local deformation may be measured to determine local contribution to ejection and/or filling based on, for example, lengthening/shortening and thickening/thinning of the heart wall and that defines a strain rate. Thus, measuring the local strain velocity provides information about the local shortening and lengthening of the heart wall. Also, determining a strain velocity provides information about the local thickening of the muscle.
The strain associated with muscle tissue generally corresponds to a ratio of the change in muscle tissue length during a time period to an initial length. In ultrasound imaging, the rate of change of strain (e.g., strain rate, strain velocity, etc.) may be visually presented to a physician as a colored segmented image, such as a bullseye plot, wherein variations in color correspond to different strain velocities. For example, strain velocity provides a direct and quantitative measure of the ability of the myocardium to contract and relax. By imaging along the myocardium from an apical view, the local strain velocity component along the long axis of the heart can be measured. By imaging from the parasternal view, the strain velocity component perpendicular to the heart wall can be determined.
Accordingly, using strain and strain rate ultrasound imaging, assessment of myocardial function may be performed. Strain measurements may be performed using different known methods to estimate cardiac deformation based on tissue deformation properties, such as tissue strain and strain velocity. However, if the determination of the strain value, for example, the tracking of the heart function is poor, such as, due to image quality (e.g., noise in the image), the calculated value may be unreliable. Thus, the display presented for review and evaluation may contain numerical values that are based on heart function tracking that is not acceptable, resulting in possible errors in evaluation and subsequent treatment.